Pour ponzu into a large, resealable plastic bag. Add albacore, seal bag, and turn fish to coat. Chill for 1 hour, turning once. Drain ponzu from bag. Add oil and turn bag to coat fish.
Heat grill to very high (550° to 650°). Oil cooking grate, using tongs and a wad of oiled paper towels.
Grill fish, covered, turning once, until grill marks appear and fish is rare, 3 minutes. Slice albacore crosswise. Fill tortillas with slaw and fish, then top with a drizzle of mayo.
*Find ponzu in the Asian foods aisle. Look for pole- or troll-caught albacore. If tortillas are very thin, buy double the amount and stack 2 per taco.
Note: Nutritional analysis is per taco with 1 tbsp. sauce.